The present invention relates to the art of tire curing. Tire curing apparatus particularly adapted for retreading relatively large off-the-road tires, such as used on heavy trucks and earth moving equipment have been employed for several years. An example is disclosed in Louis T. Fike U.S. Pat. No. 3,154,814, issued Nov. 3, 1964. Such apparatus utilizes upper and lower matrices which are vertically separable so that the lower matrix can receive the lower part of a tire to be cured. The upper matrix receives the upper part of such tire. The tire is inflated during a curing operation. Prior to a tire curing operation, the upper matrix is secured to the lower matrix by vertically extending lock arms. It is essential that such lock arms be firmly locked to the upper matrix before the tire to be retreaded is inflated. If such lock arms are not firmly locked the upper mold can be blown off the lower mold due to the high pressures developed during the curing operation. Such an accident can result in severe physical injuries as well as costly property damage.